The invention relates to a method for activating an electric motor of a metering pump.
Metering pumps functioning according to the displacement principle, thus those with a diaphragm or piston pump, are either operated electromagnetically or by way of a motor. With electromagnetically operated metering pumps the delivery quantity is usually set by mechanical stroke adjustment on the one hand and by frequency change on the other hand. In order to achieve as accurate as possible metering (admixing) of the fluid into a changeable delivery flow (main delivery flow), such pumps usually have an electrical connection to which a clock generator may be connected which always emits an impulse when a certain delivery quantity of the main delivery flow has been delivered, whereupon the metering pump executes one or more working strokes whose delivery stroke is mechanically matched to the metering quantity to be dispensed per impulse. In spite of this matching of the delivery flows to be mixed, irregular mixing ratios may occur depending on the stroke adjustment and the fluid quantity to be delivered, specifically if, for example, in a short time the fluid to be metered is to be delivered into the main flow and the next impulse is only effected after a long period of time.
Besides metering pumps with an electromagnetic drive constructed with quite a simple design, there are also known those with an electromotoric drive, for example, from DE 196 23 537 A1. Such metering pumps are much more complicated with regard to design, but permit a more exact and uniform control of the delivery quantity. Usually they function without stroke adjustment. A metering pump of this construction type is, for example, known from the type LEW A LAB K3/K5 of LEWA Herbert Ott GmbH & Co. in Leonberg. Although this pump comprises an interface for the external metering flow control, here however the activation is effected via an analog signal, which is complicated in signal processing and further processing, and is also prone to malfunctioning. The metering delivery quantity here is controlled in dependence on an electrical current.